NAT Basics Overview

NAT basics, also known as network address translation is an important part of the CCENT and CCNA certification exams. When NAT is implemented it allows a router to translate the source IPv4 address in the packet header as it crosses the router, changing the source address in the packet from one address to another. This allows the sending computer’s message to appear as if it is coming from another computer’s address. When you masquerade the origin of a computer’s IPv4 address on a network it is known as a NAT firewall.

Network address translation is a primary reason that IPv4 addressing has survived and is still in use today. The creation of NAT along with private IPv4 address ranges like 192.168.0.0 to 192.168.255.255, 172.16.0.0 to 172.31.255.255, and 10.0.0.0 to 10.255.255.255 has allowed for the conservation of publicly routable IPv4 addresses. One of the results of NAT’s ability translate public addresses at the router to private IPv4 addresses is that the advent of IPv6 addressing has essentially been delayed.

Configuring NAT

For the CCENT and the CCNA certifications you need to know how NAT works and how to configure it on a Cisco router. In the following Packet Tracer exercise and accompanying video tutorials, I demonstrate four different ways of configuring NAT.